This project evaluates the potential of erb B-2/neu immunotherapy for neoplastic disease using DNA vaccines in mice transgenic for the non-activated rat neu oncogene. These mice uniformly develop mammary tumors that express high levels of neu, and thus serve as a model for patients with cancers that overexpress erb B-2, the human neu homologue. The investigators have made plasmid vectors encoding erb B-2 (pErb B-2) or rat neu (Pneu) that induce immune responses to erb B-2 or neu when injected into muscle (IM) or dermis (ID). The investigators have found that pNeu can induce protective immunity in FVB/N non-Tg mice from the adoptive transfer of otherwise syngeneic neu- expressing mammary tumors derived from FVB/N neu-Tg mice. However, they also find that FVB/N mice have an H-2 haplotype associated with a poor immune response potential to pErbB-2/neu DNA vaccines, arguably limiting their capacity to break self-tolerance to neu in FVB/N neu-Tg mice. They have bred the neu transgene onto strains of mice that have a high response potential to pErb B-2 and pNeu (e.g. BALB/c). Preliminary studies indicate that self-tolerance to neu can be broken in neu-Tg mice with the H-2d haplotype by ID injections of pErbB-2. Work done in parallel on this project has developed improved strategies for inducing desired immune responses against the antigens encoded by DNA vaccines. The investigators find that plasmids that encode chimeric antigens that are targeted for rapid proteasome-dependent degradation are significantly more efficient in inducing specific cytotoxic T lymphocyte ( CTL) responses than conventional DNA vaccines. In addition they have found that co-injection of a DNA vaccine with the plasmid encoding the CD40-ligand (CD154) can significantly improve the immune response to a transgene antigen. They will test whether these strategies enhance their ability to break self-tolerance to neu and induce protective immunity against de novo or adoptively transferred neu-expressing mammary tumors in neu-Tg mice. In addition they will compare the relative efficacy of such DNA vaccines strategies with that of using erbB-2/neu peptide-pulsed antigen presenting cells to induce CTL against syngeneic cells expressing high levels of the erb B-2/neu proto-oncogene.